1. Field of the Invention
The present invention relates to an organic electroluminescent display (“OELD”), and more particularly, to an OELD using two panels.
2. Description of the Related Art
Organic electroluminescent displays (“OELDs”) are self-luminescent displays which use an organic compound as a luminescent material. When compared to non-luminescent thin film transistor (“TFT”) liquid crystal displays (“LCDs”), OELDs are simple and inexpensive to fabricate and have low power consumption, small thickness, and high response speed.
Active matrix OELDs include a plurality of organic light-emitting diodes (“OLEDs”) arranged in an X-Y matrix configuration and a semiconductor circuit driving the OLEDs. A conventional stack type OELD is generally a top emission type OELD. Top emission type OELDs radiate light to an outside in a direction opposite to the substrate on which the OLED is placed. In a top emission type OELD, an OLED array is disposed on a driving circuit including a plurality of transistors such that the OLED array overlaps the driving circuit. A planarization layer is formed between the OLED array and the driving circuit, and through holes are formed in the planarization layer to electrically connect the driving circuit and the OLED array.
In such a conventional stack type OELD, when an organic thin film transistor (“OTFT”) of a driving circuit is formed out of an organic semiconductor material, it may be damaged by the plasma which is used to form an OLED array on the driving circuit. While the OTFT can be formed using a low-temperature process, the OLED array is fabricated at high temperatures of 150° C. or more. When the OTFT is exposed to high-temperatures in the high-temperature OLED array fabrication process, its operating characteristics may be degraded due to damage caused by the high-temperatures.
Moreover, the driving circuit includes a switching transistor, a driving transistor, and a storage capacitor, and thus has an uneven surface. Therefore, before formation of the OLED array on the driving circuit, a planarization layer must be formed on the driving circuit in order to planarize the uneven surface of the driving circuit. Otherwise the OLED would be laid down unevenly and its electrical and light-emitting characteristics would be degraded. Also, it is necessary to form a through hole in the planarization layer in order to electrically connect the driving circuit and the OLED array.